1. Field of the Invention
The present invention concerns a thin film device of an inductor or L-C constitution which is used, for example, as a noise filter in a digital circuit and, more in particular, it relates to a thin film device attaining a high inductance by using a magnetic film having a high saturation magnetic flux density and a high permeability.
2. Description of the Prior Art
FIG. 27 is a perspective view illustrating a constitution of a dual layered spiral coil type thin film inductor in the prior art and FIG. 28 is a cross sectional view thereof.
In a thin film inductor 1 shown in FIGS. 27 and 28 a lower layer magnetic core 3 is formed on a substrate 2, and a first insulation film 4, a lower layer coil 5, a second insulation film 6, an upper layer coil 7 and a third insulation film 8 are laminated on the lower layer magnetic core 3. Then, an upper layer magnetic core 9 is disposed covering the insulation films 4, 6, 8 and the coils 5, 7 and in contact with the lower layer magnetic core 3.
FIG. 29(A) is an upper plan view of a magnetic thin film L-C filter and FIG. 29(B) is a cross sectional view thereof and FIG. 29(C) is a cross sectional view for the coil layer.
In the thin film L-C filter 11 shown in FIG. 29, a magnetic thin film inductor 12 and a thin film capacitor 13 are coupled by means of a conductor.
As shown in FIG. 29(C), the magnetic thin film inductor 12 comprises a magnetic thin film 14b and a conductor thin film 14a laminated successively on the substrate 2 in which the laminated films are formed into a planiform coil pattern. Further, the thin film capacitor 13 comprises a lower electrode 15 formed on the substrate 2, a dielectric film 16 laminated on the lower electrode 15 and an upper electrode 17 formed on the dielectric film 16. The thin film inductor 12 and the upper electrode 17 are conductively connected.
In the dual layered spiral coil type thin film inductor 1 or the thin film L-C filter 11 having the above constitution, the magnetic film has been formed so far with a permalloy (Fe-Ni system) or a Co system amorphous material in the prior art, and a saturation magnetic flux density of the magnetic material is about 1 T (Tesla). Further, the thickness of the thin film of the magnetic material in the thin film device is limited to about 1 um, the outer profile of the upper and lower magnetic cores 3, 9 or the magnetic material 14b is a rectangular shape having about 2 to 4 mm size for each one side.
In a case of constituting an inductor by forming the magnetic film having the thickness and the planiform described above by the magnetic material having the saturation magnetic flux density as described above, the inductance value is limited to about 0.1 uH. Accordingly, when the L-C filter containing the inductor is formed, the frequency for the circuit operation is in a relatively high band as 10 MHz to 100 MHz and it can not function sufficiently as a noise filter to noise components at a lower frequency.
Further, since a material of relatively low saturation magnetic flux density is used as the magnetic material, the area of the magnetic film has to be increased in order to increase the inductance value in the inductor. Accordingly, the outer size of the thin film device is increased and, further, when the magnetic material is formed into a film of a large area by vapor deposition process or the like, no high accuracy of the film thickness can be ensured.